Manufacturers in the semiconductor industry use organic materials for various fabrication steps. For example, bottom anti-reflective coatings (BARC) are used in photolithography steps to suppress reflections caused by light reflected from underlying layers, thus facilitating accurate resolution of small features. For this type of application, the BARC needs to provide conformal coverage of underlying features. In certain other applications, BARC can also serve a dual role as a planarizing layer and an anti-reflective coating. An example of a BARC is DUV 30, available from Brewer Science, Inc., located in Rolla, Mo.
Currently, one approach for providing a BARC is to synthesize a chromophore-linked novalac polymer, a cross-linker, and an appropriate solvent system. The manufacturer adds solvent to obtain the BARC viscosity necessary for producing the final thickness required by the customer's application. The manufacturer then hermetically seals the BARC within a bottle and ships it to the customer. The photolithography engineer obtains the final material form of the BARC by extracting material from the bottle, coating the substrate with the material, and baking the substrate. The organic BARC must be of appropriate thickness and optical density to actively suppress the reflective interference effects of the underlying films. In some applications, the BARC film is used to fill contact holes within a dielectric layer to an appropriate level to protect the substrate junctions during a dry etch for opening the BARC and a main etch.
More specifically, the photolithography engineer receives a package containing a BARC material. The BARC comprises a polymer component and a cross-linker component in a solvent: 
The polymer component is obtained, for example, by combining a polymer backbone, such as an epoxy novalac resin, and an actinic chromophore (see U.S. Pat. No. 5,919,598, the contents of which are incorporated herein by reference):(B) novalac epoxy resin+actinic chromophore→polymer componentTypically, the polymer component has a chromophore bonded to the backbone, or as part of the backbone design.
An example of a cross-linker component is formed by dissolving POWDERLINK® 1174 (PL 1174, commercially available from Cytec Industries Inc., located in West Paterson, N.J.) in 1-methoxy-2-propanol, and adding toluenesulfonic acid (p-TSA.H2O). The package includes PL 1174, p-TSA.H20, and alcoholic solvents such as PGME and Ethyl Lactate (EL)(see U.S. Pat. No. 5,919,599, the contents of which are incorporated herein by reference): 
FIG. 1 illustrates acid catalyzed reaction pathways in which PL and the solvents participate. The resulting mixture of PL, PL-PGME, and PL-EL adducts, shown in FIG. 1, form in solution. When the BARC formulation is applied to the silicon substrate and baked to elevated temperatures (100-220° C.), the crosslinker adducts further react with the polymer.
This combination of the cross linker component and the polymer component with a solvent is the form of the BARC needed by photolithography engineers. The chemical manufacturer may add solvents to the mixture, such as ethyl lactate, 1-methoxy-2-propanol, cyclohexanone, and n-methyl-pyrrolidone (NMP), to adjust the percentage of solids and to control the casting characteristics of the BARC, as well as to control the viscosity, and thereby control the thickness of the BARC layer when the BARC is used to coat a substrate.
It has recently been determined that in the presence of PGME and EL, the protonated PL produces PL-solvent adducts that have different structures, energies and reactivities than the starting crosslinker. FIG. 2 is a reaction scheme representing the reaction sequence in the formation of PL-PGME, and further PL-EL adducts. In the presence of p-TSA, PL will react with PGME, this intermediate further reacts to form a PL-EL adduct which is a lower energy more stable intermediate. The changes in crosslinker reactivity can be advantageously used to affect the type of coverage, e.g., conformal or planar, on the substrate.